China's latest tariffs, which follow U.S. duties on $300 billion worth of Chinese goods, threaten to prolong an ongoing trade war between the world's top two economies that has raised concerns about slowing global growth.

China's commerce ministry said it would impose additional tariffs on thousands of U.S. products, including agricultural products, crude oil, small aircraft and cars. Tariffs on some products would take effect on Sept. 1 and others on Dec. 15

"Of course China is going to retaliate. That is part of the trade war," said Scott Brown, chief economist at Raymond James, in St. Petersburg, Florida.

"Trade issues are going to be important heading into the Powell speech and he has to give some indication on how the global environment is influencing the Fed."

Powell speaks at 10 a.m. ET (1400 GMT) in Jackson Hole and investors will be looking for confirmation that the central bank will cut interest rate next month to sustain a decade long bull run for Wall Street.

At 9:41 a.m. ET, the Dow Jones Industrial Average was down 103.97 points, or 0.40%, at 26,148.27, the S&P 500 was down 12.45 points, or 0.43%, at 2,910.50. The Nasdaq Composite was down 45.05 points, or 0.56%, at 7,946.34.

Energy sector dropped 1.20%, the most among the S&P sectors, as oil prices fell.

Defensive plays were in favor as utilities was the only major S&P higher, while and real estate and consumer staples posted the smallest losses.

The biggest gainer on the S&P was Salesforce.com Inc up 5.6%, after the cloud-based service provider forecast third-quarter and full-year revenue above Wall Street estimates.

Declining issues outnumbered advancers for a 2.68-to-1 ratio on the NYSE and for a 2.39-to-1 ratio on the Nasdaq.

The S&P index recorded 21 new 52-week highs and 13 new lows, while the Nasdaq recorded 11 new highs and 41 new lows. (Reporting by Akanksha Rana, Amy Caren Daniel and Medha Singh in Bengaluru Editing by Saumyadeb Chakrabarty)